I don’t like to give arXiv.org a free pass, since it doesn’t work to the same standards as a peer-reviewed journal. But interstellar object 3I/ATLAS is moving fast, too fast for the independent review process to function. So if we don’t allow letters or preprints, ATLAS will pass us by.
Astrophysics > Earth and Planetary Astrophysics arXiv:2507.02757
[Submitted on 3 Jul 2025 (v1), last revised 7 Jul 2025 (this version, v2)]
Seligman, Darryl Z. Micheli, Marco Farnocchia, Davide et al. Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS
arXiv:2507.05252
[Submitted on 7 Jul 2025]
Bolin, Bryce T. Belyakov, Matthew Fremling, Christoffer et al. Interstellar comet 3I/ATLAS: discovery and physical description
arXiv:2507.06226
[Submitted on 7 Jul 2025]
Opitom, Cyrielle Snodgrass, Colin Jehin, Emmanuel et al. Initial VLT/MUSE spectroscopy of the interstellar object 3I/ATLAS
Have a read or three, but bear in mind that the arXiv standards are not rigorous, and everything in here is tentative (or just in need of editing).